Title: Teleconnections from the 2023/24 El Niño: Impact of long-term SST trends
Abstract
The El Niño of 2023-2024 ranked among the top 5 strongest El Niño events of the past 70 years, yet wintertime atmospheric teleconnections to the extra-tropical Northern Hemisphere were markedly weaker than anticipated. Here, we conduct a series of atmospheric modeling experiments using prescribed observed SSTs and radiative forcings to test the hypothesis that the observed pattern of background SST trends since 1980 was responsible for counteracting the expected teleconnection response. This so-called “SST pattern effect” (enhanced warming in the Tropical Indian and Atlantic Oceans and relative cooling in the eastern tropical Pacific) is shown to drive a teleconnection of the opposite sign via a Rossby wave response to anomalous precipitation over the western tropical Pacific driven remotely from the Indian Ocean. The circulation response to the 2023-2024 El Niño in the absence of background SST changes is almost entirely cancelled by the teleconnection produced by SST trends, with consequences for precipitation impacts over North America and Europe. Analogous behavior is found for the observed circulation anomalies, although internal atmospheric variability may also contribute. The results underscore the importance of considering the modulating influence of background SST trends, both natural and anthropogenic in origin, on El Niño teleconnections and associated climate impacts in the coming decades.
